1. Field of the Invention
The present invention relates to a piezoelectric bridge mounted pickup for stringed musical instruments. More specifically, the invention relates to a bridge mounted pickup which converts the vibrations of the resonating strings to an electrical signal by mechanically coupling the resonating strings to piezoelectric transducers.
2. Brief Description of the Prior Art
Since the introduction of the piezoelectric crystal microphone in the 1930's, investigators have been trying to incorporate them into musical instruments. The results were generally disappointing as the output was low and the tendency to feedback was high. Therefore, when the coil/magnet induction pickup was developed in the 1940's, it was widely adopted by musicians wanting to amplify their steel stringed instruments. Perturbations of the magnetic field caused by the resonating string results in a current induced in the coil. Therefore, these pickups measure only indirect string vibration. It is not surprising that these electro-magnetic pickups only minimally reflect the properties of the bridge and sounding board.
The piezoelectric transducer, however, can be located in a position so as to be more influenced by the acoustics of the sounding board as well as the summed interaction of the strings via the bridge. Over the last decade several investigators have patented bridge mounted piezoelectric pickups, presumably to provide increased output and decreased feedback.
Relevant examples of previous work include Murakami U.S. Pat. No. 4,211,139 to Murakami, which discloses a rigid bridge sitting directly on, and a piezoelectric element underneath, a thick vibration transmitter plate supported lengthwise by shock absorbing brackets. Another essentially rigid design is described in U.S. Pat. No. 4,491,051 to Barcus, in which a solid bridge or saddle member sits flush on top of a pickup unit which contains piezoelectric crystals. Clevinger has introduced several designs which involve a somewhat flexible bridge with essentially fixed ends. Both U.S. Pat. No. 4,567,805 and U.S. Pat. No. 4,632,002 to Clevinger describe pickups in which vibration damping pads interface between the bridge and the plate resonator, and the plate resonator and the base of the unit. U.S. Pat. No. 4,750,397 to Asbworth-Jones describes a pickup in which the periphery of a bimorphic transducer is secured via two mounting pads to the underside of the transverse bridge support, while a malleable pad or bead contacts the entire underside of the transducer and the underlying base of the unit.
Although the devices shown in most of the aforementioned patents incorporate the use of multiple piezoelectric transducers to detect the vibrations of a multitude of strings, the final output is always the sum of the individual transducers. They do not provide a switching circuit whereby the individual transducer signals can be selected or rejected selectively. The aforementioned patents also do not attempt to detect signals with different harmonic components by using resonator plates of different dimensions and by situating them under different portions of the resonating bridge including regions not directly under the strings. All of the aforementioned pickup units which incorporate bimorphic piezoelectric elements employ resonator plates supported or contacted by malleable dampeners which presumably minimize unwanted microphonics. However, the use of these dampeners results in a signal of degraded frequency range, amplitude, and sustain. Only Clevinger U.S. Pat. No. 4,567,805 and U.S. Pat. No. 4,632,002 describes pickup units which can adjust bridge/string height or can adjust for proper intonation by altering the distance between the bridge and tuning mechanism.